Ionic getter pump electrode



June 27, 1967 'r. A VANDERSLICE 3,327,930

IONIC GETTER PUMP ELECTRODE Filed Jan. 26, 1965 2 Sheets-Sheet l PRIORART INVENTOR: THOMAS A.VANDERSLICE,

AT TORNEY June 1957 T. A. VANDERSLICE ,3

IONIC GETTER PUMP ELECTRODE Filed Jan. 26, 1965 2 Sheets-Sheet 3 25FIG.4. e

FIGT.

INVENTOR: THOMAS A. VANDERSLICE,

United States Patent 3,327,930 IONIC GETTER PUMP ELECTRODE Thomas A.Vanderslice, Scotia, N.Y., assignor to General Electric Company, acorporation of New York Filed Jan. 26, 1965, Ser. No. 432,438 18 Claims.(Cl. 23069) ABSTRACT OF THE DISCLOSURE A multicellular electrodestructure for getter ion pumps wherein predetermined dimensionalcharacteristics of the m-ulticellular configuration differ to provideincreased pumping speed over a broad range of pressures.

This invention relates to an ionic pump electrode structure and moreparticularly to an improved electrode structure, for use in an ionicgetter ion pump, having a predetermined configuration including electrontransparency variations which are correlated to pumping speed and thestrength and dispersion of the cooperating magnetic field passingtherethrough.

Getter ion pumps are well known in the prior art and are adequatelydescribed, for example in US. Patents 2,775,014 Westendorp et a1. and3,080,104 Vanderslice, each of which is assigned to the same assignee asthe present invention. In one form an ionic getter pump may be describedas an envelope or an enclosure having spaced apart coaxial cathodeelements therein as an intermediate electron transparent anode, theanode and cathodes being subjected to a magnetic field having lines offorce directed substantially perpendicular to and through the anode. Inthis type of pump a glow discharge is established between the anode andthe cathode so that gas molecules in the enclosed volume are ionizedwith the resistant positive ions striking the cathode surfaces to betrapped or imbedcled therein. Also, where the cathode is ofa suitablemetal, sputtering takes place and the sputtered metal is collected orcondenses on the anode surfaces. This type of glow discharge is referredto as the Penning cold cathode discharge, described for example withrespect to pressure measuring gages in US. Patent 2,197,079 F. M.Penning. Gas cleanup in the described pump occurs through getteringaction of the fresh deposits of metal on the anode and other surface,and also by being entrapped or imbedded in these surfaces. A particularproblem associated with these getter ion pumps relates to utilization ofthe anode surfaces not only :as discharge control elements but also ascondensing or collecting surfaces for sputtered cathodic metal. Thesesurfaces should be so formed and arranged that they will control thedischarge for increased sputtering and, where applicable, receivesputtered metal in an optimum manner for increased gettering effectandentrapment action and also for wider ranges of pump speed in theliters/ sec. of gas which will be removed or pumped at a given pressure.At. the same time the anode surfaces should not adversely interfere withoptimum electrical discharge therethrough. The usual empiricalrelationship previously established for the configuration andutilization of these anodes are not s-atisfactory'for pumps of increasedspeed, efliciency and capacity.

It is an object of this invention to provide an improved electrodeconfiguration for a getter ion pump.

It is another object of this invention to provide an improved anodeelectrode configuration for a getter ion pump. 7 i

' It is still another object of this invention to provide a non-uniformanode configuration for a getter ion pump.

It is another object of this invention to provide a vari- 3,327,930Patented June 27, 1967 ice able configuration anode electrode for agetter ion pump.

It is a still further object of this invention to provide an anodeelectrode configuration for a getter ion pump which is correlated to thelines of force of and their dispersion of the magnetic field passingtherethrough.

It is a yet further object of this invention to provide an improvedcondensing or receiving surface for a getter ion pump,

Briefly described, this invention in one of its preferred forms includesa multicell-ular anode electrode structure for getter ion pumps whereinpredetermined dimensional characteristics of the multicellularconfiguration differ to provide increased pumping speed over a widerrange of pressures and where the difference is proportioned to themagnetic field passing through the multicellular structure for moreelfective pumping over the increased range This invention will be betterunderstood when taken in connection with the following description andthe drawings in which FIG. 1 illustrates a prior art Penning dischargetype getter ion pump utilizing a single cell anode structure.

FIG. 2 illustrates one preferred anode embodiment of this invention.

FIG. 3 illustrates a further anode ambodiment of this invention.

FIG. 4 illustrates a modification of FIG. 3.

FIG. 5 illustrates a further anode embodiment of this invention.

FIG. 6 illustrates another modification of this invention. FIG. 7illustrates an application of this invention in a triode pump.

The particular mode of opera-tion of the getter ion pump is based uponthe Penning discharge as above described. This discharge principle isincorporated in a Penning discharge type getter ion pump 10 asillustrated in FIG. 1 and as more fully described in the above mentionedPatent 2,755,014. The diode pump device of FIG. 1 includes an evacuatedenvelope 11 containing a pair of spaced apart disk-like cathodes 12 andan intermediate cylindrical -or ring anode 13. The anode 13 and cathodes12 are arranged concentrically along a common axis. External to theenvelope 11 there is positioned a permanent magnet14 with its polepieces also positioned concentrically along the described axis so thatthe lines of force of the magnetic field are directed perpendicularly toand through the ring anode 13. When a high positive potential withrespect to the cathodes 12 is applied to the anode 13, a gas in theenvelope 11 between the anode and cathode is ionized, permitting acurrent flow therebetween. Electrons tending to flow to the anode 13 areurged into a spiral path trajectory by the presence of the describedmagnetic field and this greatly increases the electron pat-h whichresults in a higher probability of collision between free electrons andgas molecules in the pump. A collision of an electron with gas moleculesprovides a positive gas ion. This positive gas ion is accelerated towardone of the disk cathodes 12 and strikes the cathode with great velocity,sputtering cathode metal from the cathode, to be collected on the anodeand other exposed pump surfaces. The freshly sputtered cathode metalformschemically stable compounds with active gas atoms such as oxygenand nitrogen for the pumping action. Additionally, gases are removed inthe pump by being injected into the cathode material or by being coveredwith sputtered metal on the anode and other surfaces.

In order to increase the pumping speed or capacity of the-Penningdischarge type pump as described, prior efforts have been directed tothe use of a plurality of distinct Penning discharges arranged indifferent relationships. For example, a plurality of Penning pumps maybe arranged in parallel tandem relationship so that each cathode diskbecomes in effect a cathode disk for a pair of anodes, one cathode oneach side thereof. This tandem relationship with its plural Penningdischarge increases the pumping action because a greater anode surfacearea is presented as a condensing or collecting surface for thesputtered metal. One may also arrange a plurality of Penning dischargetype pumps by inserting a plurality of the units as above described inlateral parallel spaced relationship so that there is in effect aplurality of anodes (cellular) between a pair of cathodes. In the latterinstance particularly, increased capacity is minimized because neitherthe gettering action nor the magnetic field is uniform insofar as thecross-sectional configuration of the anode is concerned. An increase insurface area does not effectively increase pumping speed over a widerpres sure range. For example, it is known that the pumping speed of apump of given geometry is constant for only a limited range ofpressures. At higher and lower pressures the pump speed generallydeclines. An increase in surface area therefore does not solve theproblem of pump speed decline at lower and higher pressures, and optimumareas of the anode for gettering purposes are, therefore, not employedto their greatest advantage.

It has been discovered that the overall pumping efficiency in liters persecond of a multicellular anode structure in a Penning discharge typegetter ion pump may be greatly increased when the configuration of theanode which is exposed to the cathode is correlated to the magneticfield passing through the anode. Referring now to FIG. 2 there isillustrated one embodiment of this invention as an anode member 15 whichis constructed so that the pump has increased pumping speed over a widerrange of pressures, and where electron transparency is cooperativelyrelated to the magnetic field passing therethrough. As previouslydescribed, the magnetic field bridging a gap between the pole pieces ofa magnet includes certain lines of force which may not be uniformlydistributed transversely through the gap. In addition, different magnetswill have different field uniformities or characteristics. It has beendiscovered that these magnetic differences have a marked effect on thepumping action of a getter ion pump utilizing multicellular anodes withcells of dimensional uniformity, and it can be seen by observation thatthe metallic deposits on these anodes are not uniformly distributedacross the anode.

When the uniformity of anode cell dimensions is varied so that the iontransparency of the anode becomes increased or decreased inpredetermined areas, an increased efficiency and higher capacity pumpingis produced. One effect is that more surface area is presented atpredetermined parts of the anode where more sputtering metal may beeffectively collected. A mixture of cell sizes is employed where somecells of predetermined size are most effective at one pressure rangewhile other cells of predetermined different sizes are most effective ata different pressure. Thus a pump is provided which includes a favorablepumping speed over a wider pressure range. At the same time thedifferent cells are arranged in more advantageous positions in the anodestructure so that their individual pumping effectiveness is increased,As one example an anode electrode incorporates predetermined groups ofcells, each group having cells of the same size but different from cellsizes of other groups. Such elec trodes are effectively utilized inuniform or non-uniform magnetic fields and are two-fold in nature inthat 1) the variation of cell size is chosen for example toincreasepumping characteristics, for example, a given large cell size providesoptimum pumping at a given pressure and a given small cell size providesoptimum pumping at a different given pressure, and (2) based on (1) thevariation in cell size or distribution is again chosen and arranged formore effective pumping for non-uniform mag netic fields. There isaccordingly a two-step predetermination involved. As a part of thetwo-step predetermination,

however, it will be apparent that the product of a cell opening diameter(in the case of a cylindrical cell) to the strength of the magneticfield passing therethrough will not be optimum as is usually desired. Incontradistinction the product will be optimum or approaching optimum forthe primary purpose of, in combination with adjacent different sizecells, increasing the pumping speed over a wide range of pressures ormaintaining a more constant pumping speed for a wider range ofpressures.

In FIG. 2, anode 15 which may be of any desired overall cross-sectionalconfiguration such as circular or polyhedral includes a plurality ofindividual cells 16 which are formed for example by bounding means inthe form of slat members 17. The cooperative relationship of these slatsdefines individual cells 16 having a depth or dimen sion along theirlongitudinal axis preferably at least equal to an opening dimension.This opening may take the form of various geometric or irregular orcombined perimeter designs such as for example arcuate, circular,square, polygonal, etcetera, or combinations thereof. It is an importantfeature of anode 15 that the electron transparency of the cells is notuniform or similar for each cell. The non-uniformity is illustrated inone manner by different cell sizes in the outer or peripheral row,although a plurality of similar cell sizes may exist in one peripheralrow. In this particular embodiment, while there is an overall uniformgradation radially, i.e., cells 18, 19 and 20, other directionalindications are non-uniform. It is this superimposition of oneconfiguration over another which is important to this invention. Becauseof the many variations in a given magnetic field or a given pump anorderly peripheral distribution of different cell sizes is preferred asillustrated in FIG. 2 noting the perimeter row of cells. However, thedistribution may be random if desirable. A variation in cell size isintended to include a difference in any dimension of the cell or wallsthereof, its area or volume. The difference may be included in one ormore cells with the variation among cells being regular, irregular,progressively uniform, interrupted, concentrated, localized, or random.The difference employed, however, must be effective for changing thepumping speed and capacity of the pump. In the slat type assem* bly asillustrated, minor mechanical changes of position will provideinnumerable combinations of variations in cell sizes for optimumcorrelation with pumping speed range and applied magnetic field.

A further example of a variable cell anode is illustrated in FIG. 3,Referring now to FIG. 3, there is shown an anode 21 having a center areaor group of cells 22 made up of a plurality of large cells 23 of onesize and a surrounding area or group of smaller cells 24. In thisembodiment the cell size may be referred tothe opening area of theindividual cells. An important feature of the embodiment of FIG. 3 isthe superimposition of two kinds of cells for two different purposes asdescribed for FIG. 2. The overall configuration of anode 21 is that of aplurality of adjacent cells 23, each cell 22 having an adjacent similarcell on at least two sides. However, an outer perimeter row of cells 23have been subdivided to provide smaller cells 24. Smaller cells 24 alsohave an adjacent similar cell on at least two sides. Anode 21 is thus atwo-stage anode which partially compromises high capacity at a givenpressure for increased pumping speed over a wider range, a moredesirable mode of operation in many instnaces. The particular choice ofan anode as illustrated in FIG, 2 or that as illustrated in FIG. 3 willdepend on the pump configuration, magnet arrangement and configurationand magnetic field distribution. However, it is desirable that in atwo-stage anode two substantial areas of similar cells are included, oras in FIG. 2, the superimposition results in substantial cell sizedifferences in peripheral as well as radial directions.

In FIG. 4 there is illustrated an anode 25 having localized cell sizevariation opposite to that as illustrated in FIG. 3. In FIG. 4, anode 25is made up of a group of similar cells 26 which are of optimum 'size fora given pump speed. Superimposed on anode 25 is a central sec tion 27 ofsmaller similar cells 28 which are of optimum size for a further pumpspeed. The particular cells of any of the anodes of this invention neednot be for example polygonal as anode may contain both polygon andcircular cells or various combinations of regular or irregular cells.For example, cylindrical may fit within or contain polygon cells. Inconnection with the FIG. 4 illustration as a reversal of the FIG. 3illustration, the illustration of FIG. 2 may also be reversed.

FIG. 5 is an illustration of a further embodiment of this invention. InFIG. 5, electrode 29 includes a combination of concentric ornon-concentric annular elements 30, 31, 32, 33 and cross slats 34. Theannular elements have proportionate diameters which provide closerspacings between elements radially. The reverse configuration is alsoevident. The cross slats 34 are an additional superimposition onincluded concentric cylinder combinations and are utilized not only forsupport purposes but also to establish cell sizes for a given pumpingspeed. In FIG. 5 the electrode configuration may be provided by means ofa spiral strip which is so wound to provide the desired variation.

In addition to varying the electron transparency of a multicellularelectrode by changing one or more cell opening sizes, certain othermodifications may be suitably employed to provide similar results. Forexample, the electrode structure 35 of FIG. 6 includes a forward face 36and a rearward face 37. These faces are illustrated as inwardlyoutwardly tapered curved or disked. The effect of this curvature is tochange the longitudinal or depth dimension of individual cells with aresultant change in the effectiveness of the cell. The curvature of thefaces 36 and 37 of electrode 35 are merely exemplary of the many bothsmooth and interrupted configurations which may be utilized inconjunction with these faces to increase favorable pumpingcharacteristics. Where desirable, the

magnet pole pieces utilized may have similarly shaped.

faces in apparent interfitting relationship with the anode.

One operative example of the practices of this invention is illustratedin connection with the triode ion pump of FIG. 7. Referring now to FIG.7 triode pump 38 includes a central multicellular anode 39 and a pair ofspaced multicellular cathodes 40 and 41. The practices of this inventionmay be applied to the cathodes 40 and 41 as well as to the anode 39. Inone example one or more central cells of each electrode, i.e., anode andcathodes, is of a similar size and all are in axial alignment. Cellsizes then may be varied as illustrated in FIGS. 2 through 6. f

Accordingly, by practices of this invention a multicellular ion pumpelectrode structure may be specifically correlated pumping speed and tothe magnetic field passing therethrough and also to concentration ofsputtered metal at certain regions of the anode. The teachings of thisinvention as described may also be incorporated in an anodemulticellular structure having means to vary the positional relationshipof the anode or individual portions thereof with respect to the cathodesand to the magnetic field. For example, certain elements such as theslats may be adjusted or otherwise positionally changed so that theircross-sectional configuration directly exposed to the cathode ischanged, or various parts of the anode may be mechanically adjusted tochange their relative position. The mechanics involved relate to wellknown adjusting devices in the art such as blade and vane pitchadjusting devices and controls, irises, gates, et cetera. Such changesmay be employed to adjust the speed or pumping range of the pump.

The objects of this invention are attained through the use of variation,broadly, of electrode transparency which is cooperatively correlated topumping speed and to the applied magnetic field. In one preferredpractice of this invention the. variation in cell size enables the pumpto include optimum and more consistent pump speeds at diiferentpressures thus taking advantage of the different disclosure.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

1. In an ionic getter pump having an ion transparent anode electrodepositioned adjacent a cathode electrode and submerged in a magneticfield passing in a direction from one of said electrodes to the other,said electrodes having a potential impressed thereon to provide adischarge therebetween so that cathode metal is sputtered for getteringaction, the improvement comprising (a) one of said electrodes includinga multiplicity of individual cells of at least two different sizeseffective to alter the pumping characteristics of said pump,

(b) said cell sizes being predeterminedly optimumly correlated topumping speed thereof and to the nonunifor mity of the magnetic fieldpassing therethrough,

(c) a significant number of said cells of one size having optimumpumping characteristics in conjunction with a high intensity magneticfield being exposed'to a substantial lower intensity magnetic field,

(d) a significant number of said cells of the other size having optimumpumping characteristics in conjunction with a low intensity magneticfield being exposed to a substantial higher magnetic field,

(e) so that a favorable pumping speed of said pump is extended over awider range of pressures.

2. The anode asrecited in claim 1 wherein said electrode is an anodeelectrode.

3. The invention as recited in claim 1 wherein said electrode is acathode electrode.

4. The invention'as recited in claim 1 wherein said electrode includesan anode and a cathode electrode.

5. The invention as recited in claim 1 wherein said cell size is denotedby a cell opening dimension.

6. The invention as recited in claim 1 wherein said cell size is denotedby a cell depth dimension.

7. The invention as recited in claim '1 wherein said cells are arrangedto include an interspersed order. 8. The invention as recited in claim 1wherein said cells are arranged in distinct groupings.

9. In an ionic getter pump having an ion transparent anode electrodepositioned adjacent a cathode electrode and submerged in a magneticfield passing in a direction from one of said electrodes to the other,said electrodes having a potential impressed thereon to provide aPenning discharge therebetween so that cathode metal is sputtered onsaid anode for gettering action, the improvement comprising (a) one ofsaid electrodes including a multiplicity of individual cells of at leasttwo different sizes effective to alter the pumping characteristics ofsaid pump,

(b) said cell sizes being arranged in at least two distinct groupshaving the same cell size in each not found in the other,

(e) one of said groups encircling the other,

(d) said cell sizes being predeterminedly optimumly correlated topumping speed thereof and to the nonuniformity of the magnetic fieldpassing therethrough,

(e) so that a favorable pumping speed of said pump is extended over awider range of pressures.

10. The invention as recited in claim 9 wherein said electrode is ananode electrode and (a) the first group of said cells being centrallyarranged in a regular order of differing cell sizes,

(b) the second group of said cells encircling said first group andcomprising at least a row of cells of differing sizes.

11. In an ionic getter pump having an ion transparent anode electrodepositioned adjacent a cathode electrode and submerged in a magneticfield passing in a direction from one of said electrodes to the other,said electrodes having a potential impressed thereon to provide aPenning discharge therebetween so that cathode metal is sputtered onsaid anode for gettering action, the improvement comprising (a) one ofsaid electrodes including a multiplicity of individual cells of at leasttwo different sizes effective to alter the pumping characteristics ofsaid pump,

(b) said cell sizes being predeterminedly optimumly correlated topumping speed thereof and to the nonuniformity of the magnetic fieldpassing therethrough,

(c) the cells of said electrodes being arranged so provide a centralgroup of cells of similar size,

(d) an adjacent group of cells of similar cell size and (e) the cellsize of one of said groups differing from the cell size of the othersaid group so that said electrode is operative to increase the pumpingspeed of said pump over a wider range.

12. The invention as recited in claim 11 wherein said electrode is ananode electrode and said adjacent group of cells comprises at least tworows of cells encircling said central group.

13. In an ionic getter pump having an ion transparent anode electrodepositioned adjacent a cathode electrode and submerged in a magneticfield passing in a direction from one of said electrodes to the other,said electrodes having a potential impressed thereon to provide aPenning discharge therebetween so that cathode metal is sputtered onsaid anode for gettering action, the improvement comprising (a) one ofsaid electrodes including a multiplicity of individual cells of at leasttwo different sizes effective to alter the pumping characteristics ofsaid pump,

(b) said cell sizes being predetermined optimumly correlated to pumpingspeed thereof and to the non-uniformity of the magnetic field passingtherethrough,

(c) the openings of said cells having different geometricalconfigurations comprising the combination of arcuate and rectilinearsides,

(d) so that a favorable pumping speed of said pump is extended over awider range of pressures.

14. The invention as recited in claim 13 wherein said electrodecomprises a series of concentric cylinders and cross members.

15. In an ionic getter pump having anion transparent anode electrodepositioned adjacent a cathode electrode and submerged in a magneticfield passing in a direction from one of said electrodes to the other,said electrodes having a potential impressed thereon to provide aPenning discharge therebetween so that cathode metal is sputtered onsaid anode for gettering action, the improvement comprising (a) one ofsaid electrodes including a multiplicity of individual cells of at leasttwo different sizes effective to alter the pumping characteristics ofsaid pump,

(b) said cell sizes being predeterminedly optimumly correlated topumping speed thereof and to the nonuniformity of the magnetic fieldpassing therethrough,

(c) the said cell sizes having differences limited to an axial dimensionthereof,

((1) so that a favorable pumping speed of said pump is extended over aWider range of pressures.

16. The invention as recited in claim 15 wherein the said cells haveuniform progressively differing depth dimensions.

17. The invention as recited in claim 15 where the said differencesprogress radially. p

18. In a triode ion getter pump having an ion transparent electrodepositioned between spaced ion transparent cathodes Where said electrodesare submerged in a magnetic field passing in a direction generallyperpendicularly through said electrodes and said electrodes having apotential impressed thereon to provide a Penning type dischargetherebetween so that cathode metal is sputtered on said anode forgettering action, the improvement comprising (a) said anode and saidcathodes each including a multiplicity of individual cells of at leasttwo different sizes effective to alter the pumping characteristics ofsaid pump,

(b) said cell sizes being predeterminedly optimumly correlated topumping speed thereof and to the nonuniformity of the magnetic fieldpassing therethrough,

(c) so that a favorable pumping speed of said pump is extended over aWider range of pressures.

References Cited UNITED STATES PATENTS 3,141,986 7/1964 Lloyd 23069ROBERT M. WALKER, Primary Examiner.

LAURENCE V. EFNER, Examiner.

1. IN AN IONIC GETTER PUMP HAVING AN ION TRANSPARENT ANODE ELECTRODEPOSITIONED ADJACENT A CATHODE ELECTRODE AND SUBMERGED IN A MAGNETICFIELD PASSING IN A DIRECTION FROM ONE OF SAID ELECTRODES TO THE OTHER,SAID ELECTRODES HAVING A POTENTIAL IMPRESSED THEREON TO PROVIDE ADISCHARGE THEREBETWEEN SO THAT CATHODE METAL IS SPUTTERED FOR GETTERINGACTION, THE IMPROVEMENT COMPRISING (A) ONE OF SAID ELECTRODES INCLUDINGA MULTIPLICITY OF INDIVIDUAL CELLS OF AT LEAST TWO DIFFERENT SIZESEFFECTIVE TO ALTER THE PUMPING CHARACTERISTICS OF SAID PUMP, (B) SAIDCELL SIZES BEING PREDETERMINEDLY OPTIMUMLY CORRELATED TO PUMPING SPEEDTHEREOF AND TO THE NONUNIFORMITY OF THE MAGNETIC FIELD PASSINGTHERETHROUGH, (C) A SIGNIFICANT NUMBER OF SAID CELLS OF ONE SIZE HAVINGOPTIMUM PUMPING CHARACTERISTICS IN CONJUNCTION WITH A HIGH INTENSITYMAGNETIC FIELD BEING EXPOSED TO AS SUBSTANTIAL LOWER INTENSITY MAGNETICFIELD, (D) A SIGNIFICANT NUMBER OF SAID CELLS OF THE OTHER SIZE HAVINGOPTIMUM PUMPING CHARACTERISTICS IN CONJUNCTION WITH A LOW INTENSITYMAGNETIC FIELD BEING EXPOSED TO A SUBSTANTIAL HIGHER MAGNETIC FIELD, (E)SO THAT A FAVORABLE PUMPING SPEED OF SAID PUMP IS EXTENDED OVER A WIDERRANGE OF PRESSURES.